1. Field of the Invention
The present invention relates to a gas filled switching electric discharge tube. More particularly, the present invention relates to the structure of a gas filled switching electric discharge tube in which the voltage characteristic at the time of electric discharge is improved.
2. Related Art
The gas filled switching electric discharge tube includes: a cylindrical body made of an insulating material such as a ceramic; and a first and a second electrode for airtightly closing both ends of the cylindrical body, wherein an electric discharge gap is formed between the first electrode face of the first electrode and the second electrode face of the second electrode, and gas is filed into an airtightly closed space which is formed in the cylindrical body including the electric discharge gap. Due to the above structure, electric discharge is generated between the first electrode face and the second electrode face.
In the case where switching is conducted in the thus composed conventional switching electric discharge tube after it has been left in a completely dark place, the electric discharge voltage (FVs) of the first discharge is necessarily higher than electric discharge voltage (Vs) of the second discharge and following discharges. The reason why is that, as the switching electric discharge tube has been left in a dark place, it is impossible for photo-electrons, which always excite the filled gas in a bright state, to provide an excitation effect (photo-electron effect).
Conventionally, the life of electric discharge of the electric discharge tube has been extended and an increase of the FVs characteristic, in a life test, has been prevented by arranging carbon trigger wires on an inner wall face of the cylindrical body made of ceramic and devising various methods of arrangement.
For example, in order to improve the voltage characteristic of this type switching electric discharge tube in the case of discharg, the following arrangements have been proposed. Metalized faces are formed on both end faces, which come into contact with the electrodes, of the cylindrical body made of ceramic, and trigger wires are provided which come into contact with the metalized faces and extend on an inner wall face of the cylindrical body or, alternatively, trigger wires are provided which do not come into contact with the metalized faces but extend on the inner wall face of the cylindrical body. Referring to FIGS. 11 and 12, the arrangement of these carbon trigger wires will be explained below.
FIGS. 11 and 12 are views of the development of an inner wall face of the cylindrical body made of ceramic. In FIG. 11, the trigger wires 10a, 10b are extended from the metalized faces in the axial direction of the cylindrical body and arranged at regular intervals of 90xc2x0. In this case, the trigger wires are arranged at regular intervals of 90xc2x0 on one metalized face 12 side and also arranged on the other metalized face 14 side alternately. The central trigger wires 10c are respectively arranged in the axial direction at regular intervals of 90xc2x0 at the intermediate positions between the trigger wires 10a 10b which extend from the metalized faces.
In FIG. 12, the trigger wires 10a, 10b, the number of each of which is two, extending from the metalized faces in the axial direction are arranged close to each other. Other structural arrangements are the same as those of the case shown in FIG. 11.
In order to extend the life of electric discharge, it is necessary to reduce the number of the trigger wires coming into contact with the metalized faces. However, when the number of the trigger wires is reduced, there is caused an undesirable problem whereby FVs is raised. Further, when only the carbon trigger wire arrangements are devised, the effects of extending the life of electric discharge and preventing an increase of the FVs characteristic, in a life test, which must be compatible with each other, are limited.
In view of the limitation on compatibility of extending the life of electric discharge with preventing an increase in the FVs characteristic in the life test only when the carbon trigger wires are formed in the cylindrical body or only when the carbon trigger arrangements are devised, this invention has been accomplished.
Accordingly, it is an object of the present invention to provide a gas filled switching electric discharge tube capable of accomplishing the extension of the life of electric discharge and also capable of accomplishing the prevention of an increase in the FVs characteristic in the life test by improving an electric discharge gap and a profile of the electrode face.
In the first embodiment of the present invention, there is provided a gas filled switching electric discharge tube comprising: a cylindrical body made of an insulating material; a first electrode and a second electrode for airtightly closing both ends of the cylindrical body; an electric discharge gap formed between a first electrode face of the first electrode and a second electrode face of the second electrode, an airtightly closed space formed in the cylindrical body being filled with gas; metalized faces formed on both end faces of the cylindrical body, the first and the second electrode being joined to the cylindrical body on both end faces of the cylindrical body; first trigger wires formed on an inner wall face of the cylindrical body, connected with the metalized faces; and second trigger wires formed on the inner wall face of the cylindrical body, not connected with the metalized faces, wherein the number of the second trigger wires is larger than the number of the first trigger wires, an interval of the electric discharge gap is made to be larger than a distance from the second trigger wires to the first or the second electrode face, and a plurality of recess portions are formed on the first electrode face of the first electrode or the second electrode face of the second electrode.
In the second embodiment of the present invention, there is provided a gas filled switching electric discharge tube comprising: a cylindrical body made of insulating material; a first electrode and a second electrode for airtightly closing both ends of the cylindrical body; and an electric discharge gap formed between a first electrode face of the first electrode and a second electrode face of the second electrode, an airtightly closed space formed in the cylindrical body being filled with gas, wherein an interval of the electric discharge gap is made to be larger than a distance from the second trigger wires to the first or the second electrode face, and a plurality of recess portions are formed on the first electrode face of the first electrode or the second electrode face of the second electrode.
In the third embodiment of the present invention, there is provided a filled switching electric discharge tube comprising: a cylindrical body made of insulating material; a first electrode and a second electrode for airtightly closing both ends of the cylindrical body; an electric discharge gap formed between a first electrode face of the first electrode and a second electrode face of the second electrode, an airtightly closed space formed in the cylindrical body being filled with gas; metalized faces formed on both faces of the cylindrical body, the first and the second electrode being joined to the cylindrical body on both the end faces of the cylindrical body; first trigger wires formed on an inner wall face of the cylindrical body, connected with the metalized face; and second trigger wires formed on the inner wall face of the cylindrical body, not connected with the metalized face, wherein the number of the second trigger wires is larger than the number of the first trigger wires, and a plurality of recess portions are formed on the first electrode face of the first electrode or the second electrode face of the second electrode.
In the fourth embodiment of the present invention, there is provided a gas filled switching electric discharge tube comprising: a cylindrical body made of insulating material; a first electrode and a second electrode for airtightly closing both ends of the cylindrical body; an electric discharge gap formed between a first electrode face of the first electrode and a second electrode face of the second electrode, an airtightly closed space formed in the cylindrical body being filled with gas; metalized faces formed on both end faces of the cylindrical body, the first and the second electrode being joined to the cylindrical body on both the end faces of the cylindrical body; first trigger wires formed on an inner wall face of the cylindrical body, connected with the metalized faces; and second trigger wires formed on the inner wall face of the cylindrical body, not connected with the metalized faces, wherein the number of the second trigger wires is larger than the number of the first trigger wires, and an interval of the electric discharge gap is made to be larger than a distance from the second trigger wires to the first or the second electrode face.
The cylindrical body is a cylinder, the first and the second electrode face are substantially circular and formed around the central axis of the cylindrical body, the first and the second electrode face are arranged being symmetrically opposed to each other, the first trigger wires extend from the metalized faces in the axial direction on the inner wall face of the cylindrical body, however, the first trigger wires do not reach a central portion of the cylindrical body, and the second trigger wires extend in the central portion of the cylindrical body in the axial direction.
In this case, the first trigger wire extending from one metalized face on the inner wall face in the axial direction and the first trigger wire extending from the other metalized face on the inner wall face in the axial direction are arranged being formed into a pair at an interval of 180xc2x0.
In this case, the pair of the first trigger wires are respectively composed of a plurality of trigger wires arranged close and parallel to each other, and the pair of the first trigger wires are respectively composed of 2 or 3 trigger wires arranged close and parallel to each other.
The length of the first trigger wire in the axial direction is not more than ⅓ of the length of the cylindrical body in the axial direction.
A plurality of the second trigger wires are arranged at substantially regular intervals between a pair of the first trigger wires which are arranged at an interval of 180xc2x0, and the length of the second trigger wire in the axial direction is not less than xc2xd of the length of the cylindrical body in the axial direction.
The cylindrical body is a cylinder, the first and the second electrode face are substantially circular and formed around the central axis of the cylindrical body, the first and the second electrode face are arranged being symmetrically opposed to each other and the first trigger wires extend from the metalized face in the axial direction on the inner wall face of the cylindrical body. However, the first trigger wires do not reach a central portion of the cylindrical body, the second trigger wires extend in the central portion of the cylindrical body in the axial direction, and a distance from the second trigger wire to the first or the second electrode face is the same as a distance from an outer circumference of the electrode face to an inner wall of the cylindrical body in the radial direction. An interval of the electric discharge gap is the same as a distance between an end portion of the first electrode face and an end portion of the second electrode face.
A plurality of recess portions provided on the first or the second electrode face are respectively a hemispherical recess portion. In this case, the plurality of recess portions are uniformly arranged at regular pitches of 0.1-1.0 mm. The first and the second electrode face are arranged being symmetrically opposed to each other, central portions of the electrode faces are hollowed with respect to the peripheral portion, and the plurality of recess portions are formed in the hollow portion.
The cylindrical body is made of ceramic, and the first and the second electrode are made of iron-nickel alloy such as 42-alloy or iron-nickel-cobalt alloy such as covar. The first and the second electrode are joined to the cylindrical body by means of soldering.